DS is 20 months old. we have a potty. he likes to follow us to the bathroom and sit on it whenever we go on the toilet.
the other day i let him go diaperless and he peed on the floor, and I told him what it was, told him we go on the potty- we cleaned it up, and then he sat on the potty half naked of his own accord (the next time I sat on the toilet though)
is it a good idea to do these things even though I know he isnt ready yet? will it help him to be ready?

Yes, it's a very good idea. And yes, it will help him to potty-learn sooner. The more you talk about it with him, the more you build his awareness about his elimination. I also recommend reading the book, Diaper-free before 3. It's the most logical and research-based book I've found regarding potty-training (either early OR late).

What makes you think he isn't ready yet? This is pretty much exactly how we went about PTing. The accidents on the floor were what really gave my DS a real boost. He very quickly made the connection between the sensation of peeing and its result. When they're going in their diaper they really don't know exactly what's happening down there. So I think this approach is a great one. We started around 19 months and by about 21 or 22 months my DS was in underwear full time.

what makes me think he isnt ready? I'm not sure he understands that he's peeing when he pees on the floor. however we had success today- got a pee in the potty. gave him a big high 5, had him wipe and flush, - so that was good.

however Dh has a big problem with my leaving him naked. so can you recommend something we could pull up and down, and Ds would feel wet- but there wouldnt be a big puddle on the floor.
that being said- would that even work- or is peeing on the floor sort of necessary to "get it?"

No I don't think so. We used thick cloth training pants with DD. We used Eco Nix, but those are hard to find now, but I know there are other brands. They were thick enough there was no puddle on the floor but they don't make the pee practically vanish into thin air like a disposable does, so she really felt WET when she peed. Usually she would have to change her clothes after an accident.

Just one caution, you can want him to potty learn early, but just don't let it become a pressure thing for you or for him. Some kids just take a long time, even if EC'd full time from birth. The only thing you can do is provide the opportunity, and if he takes it, then great, if he doesn't, he'll do it in his own good time.

I don't think peeing on the floor is necessary in order for him to get it, but I think it could potentially have the biggest impact. And he may not know that THAT is pee when he does it, but that's where you come in and tell him. He'll likely catch on really quick. We didn't do the bare bum time for too long. It was maybe a week or two. By that point we were starting to have more and more successes on the potty and so I wanted to move on and have DS get used to wearing something on his bum but not doing his business in it. We skipped trainers and went straight to underwear for around the house. I asked DS if he needed to use the potty and took him there every 1-3 hours during the day. Consistently telling me that he had to go before he actually went in his pants was the last step (for my DS anyway). So don't get discouraged if that doesn't come anytime soon. It doesn't mean your LO isn't making progress. Personally, I think that learning to recognize what their body is telling them and also learning to control their bladder and bowels is more impressive. I think those skills are often underrated and under appreciated when it comes to tots just learning to use the potty.

i'm not trying to push him. he seems interested- so i'm trying to run with it. we had quite a good success yesterday. at first I felt like I was driving the two of us crazy, i knew he needed to poop. so I convinced him many times to sit on the potty; and finally he pooped on the potty. but the best part was later that evening, he farted, yelled "caca" and ran to the bathroom and sat himself on the potty. he didnt actually need to caca but I love that he made the association. at the moment I want some kind of pull-up just to make it easier on me. cause when he's naked, he runs away, and then wiggles like crazy while I try to put his diaper on.